Measuring Surface Deformation Caused by Permafrost Thawing Using Radar Interferometry, Case Study

Abstract

Permafrost in high-arctic regions has been very much influenced by global warming. Many thousands of square kilometers of permafrost are under certain degree of thawing. Site measurements have provided useful data for researchers. However, these ground-based measurements are usually site-specific with poor spatial coverage. Here we apply Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) to measure the surface deformation over permafrost north-east Greenland during the past two periods 1995--1999 and 2006--2009 to infer permafrost behaviors. We have found a considerable rate of surface subsidence occurring with respect to a relatively stable area. Over the whole study area, during 1995--1999, we find a surface subsidence rate of 0.3--2.4 mm/yr and a seasonally varying displacement of 0.4--6.1 mm with subsidence occurring during the thawing season of each year. While in period of 2006--2009, we find the overall surface subsidence rate goes up to 0.8--2.7 mm/yr and the seasonally varying displacements increased to 2.3--7.4 mm within the thawing season. Comparing with the two periods, we find a general accelerating trend in subsidence rate of 4.5 x 102 mm/yr2, which indicates a acceleration in permafrost thawing rate. We also find a general increment in surface seasonal varying displacements of 1.9 mm, which indicates a thickening trend in the active layer. In total, by applying MT-InSAR technique over the 5000 km2 study area, we have found a permafrost area 506.1 km2 of that is under thawing and the general magnitude of permafrost thawing rate is 17.0±8.4 cm/yr during 1995--1999. During 2006--2009, we have found 633.9 km2 of permafrost area is thawing with a magnitude of thawing rate about 24.0±12.0cm/yr. We have also estimated the total volume loss of permafrost as (2.1±1.1) x 108 m2 and (3.0±1.5) x 108 m3 in each corresponding period. Further, assuming the linear relationship between the thawed permafrost and the released methane fluxes observed during 19-Jun-1997 to 18-Aug-1997 at Zackenberg valley, we apply this relationship to the whole subsidence area. We estimate the total magnitude of methane fluxes released from the study area within this period, which is about 1081.7±398.5 T.